1. Field of the Invention
The present invention relates to an electrostatic latent image forming method, an electrostatic latent image forming apparatus, and an image forming apparatus, and more particularly to an electrostatic latent image forming method and an electrostatic latent image forming apparatus for forming electrostatic latent images by using light and to an image forming apparatus that includes the electrostatic latent image forming apparatus.
2. Description of the Related Art
In recent years, the image forming apparatuses capable of forming images in multiple colors have been used for simple printing in an on-demand printing system, and there is a demand for higher-quality images.
For higher-quality images, there is a need to correctly form multiple dots included in an image in accordance with image information, i.e., achieve superior dot reproducibility.
Electrophotographic image forming apparatuses perform a plurality of processes, i.e., a charge process, exposure process, developing process, transfer process, fixing process, or the like, and the quality of the finally output image is highly affected by the accuracy of each of the processes. Particularly, the state of an electrostatic latent image formed on a photosensitive element during an exposure process is important as it directly affects the behavior of toner particles during a developing process.
Therefore, there is a need to correctly form electrostatic latent images in accordance with image information.
For example, Japanese Patent Application Laid-open No. 09-85982 discloses an exposure method performed by a laser beam printer that features printing by changing the amount of irradiation light for a signal dot to be printed in accordance with the number of dots that are adjacent to the single dot to be printed on the left, right, top, and bottom thereof.
Japanese Patent Application Laid-open No. 2004-181868 discloses an image forming apparatus that is characterized in that, if there is a small number of “pixels on which toner is to be formed” in the N×M area in the vicinity of an arbitrary pixel within the image to be printed, the amount of irradiation light for the image is controlled so that “the electric field intensity for developing the toner is increased” and, if there is a large number of “pixels on which toner is to be formed” in the N×M area in the vicinity of the pixel, it is controlled so that “the electric field intensity for developing the toner is decreased”.
Furthermore, Japanese Patent Application Laid-open No. 2009-37283 discloses an image processing apparatus that is characterized in that it includes an image-signal input unit that receives an input of an image signal of the image to be processed; a density-reduced area detection unit that uses the image signal input to the image-signal input unit to detect, from the image to be processed, a density-reduced area that satisfies a predetermined image density reduction condition; a specific-image area detection unit that uses the image signal input to the image-signal input unit to detect, from the image to be processed, a specific image area that satisfies a predetermined specific-image condition that is different from the predetermined density reduction condition; and a density control unit that, with respect to a non-specific image area other than the specific image area detected by the specific-image area detection unit, performs a density reduction operation to reduce the image density of the density-reduced area that is detected by the density-reduced area detection unit and that, with respect to the specific image area, does not perform the density reduction operation on the density-reduced area even if the density-reduced area is included therein.
Furthermore, Japanese Patent No. 3733166 discloses a multicolor output device that is characterized in that it includes an image generation unit that generates a bitmap image in each color; an image carrier that has a latent image formed on its surface due to the distribution of an electric potential; a latent-image forming unit that refers to the pixel of interest in the bitmap image and a group of pixels in the vicinity thereof and that, if the pixel of interest is a white pixel and the group of pixels in the vicinity of the pixel of interest includes a pixel that is not white, forms a latent image corresponding to the pixel of interest on the image carrier by using the electric potential that has a predetermined difference from the electric potential corresponding to a white pixel and that does not develop it; and a developing unit that develops the latent image on the image carrier.
However, with the method and apparatuses disclosed in Japanese Patent Application Laid-open No. 09-85982, Japanese Patent Application Laid-open No. 2004-181868, Japanese Patent Application Laid-open No. 2009-37283, and Japanese Patent No. 3733166, it is difficult to form electrostatic latent images of required quality.